text:
What is the correct crew procedure for an unreliable airspeed alert?
When the crew receives "airspeed disagree" message on the primary flight displays, they may face some hazardous situation.
Is there any procedure, using a table containing pitch, power, altitude and weight, to avoid stall, for example?

This has the exact same answer as your other question about altimeters, so you may just want to ask one about "unreliable flight instruments" instead of one for each of the different instruments...

TURN ON THE PITOT HEAT!

As you probably know this is the situation that occurred for AF-447 (Rio-Paris) on June 2009. From the BEA report:

The accident resulted from the following succession of events:

Temporary inconsistency between the measured airspeeds, likely following the obstruction of the Pitot probes by ice crystals that led
in particular to autopilot disconnection and a reconfiguration to
alternate law, [...]
The crew not making the connection between the loss of indicated airspeeds and the appropriate procedure,

This mistake happened previously. From the same report:

Four crews did not identify the unreliable airspeed  situation: in two
cases, the crews concluded that there was an inconsistency between the
angles of attack; in the two other cases, the crew considered that the
speeds were erroneous rather than unreliable.

Then the procedure that should be used in case of unreliable airspeed:

The philosophy for processing the anomaly is described in the
“UNRELIABLE AIRSPEED INDICATION / ADR CHECK PROCEDURE” that is in
Flight Manual (AFM) and transcribed in the Airbus FCOM and the Air
France Operations Manual.

This procedure which is to be known without the support of the documentation gives time to retrieve data from the documentation (this is what you wanted to know):

See also:

Unreliable Airspeed Indications on SKYbrary.

What does "THRUST RED ALT" mean?

@Ben: Thrust reduction altitude. The altitude at which the pilot reduces thrust after take-off.

Makes perfect sense to me now, thanks


text:
What's the correct ATC phraseology to enter a nonpublished hold?
Before entering on a hold (stack), the ATC should instruct the turns and headings to be accomplished by the crew.  If it is not printed on the charts, as on STARs, what is the correct phraseology to be used by ATC?

In the US e.g. ATC will say " hold east of Miami VOR", meaning you hold on Radial 090 right turns, 1 minute leg. In most of the rest of the wold ATC will give you the inbound course unless stated on the chart.

You didn't mention any particular country or jurisdiction, but for the US the FAA's ATC orders say in section 4-6-4:

PHRASEOLOGY−
   HOLD (direction) OF (fix/waypoint) ON (specified radial, course, bearing, track, airway, azimuth(s), or route.)
If leg length is specified,
  (number of minutes/miles) MINUTE/MILE LEG.
If
  direction of turn is specified,
  LEFT/RIGHT TURNS.

source: Stack Exchange

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sort: votes


text:
Why do I see moisture coming from the middle of the wing as well as wingtip vortices?
A lot of times I see small tube like streams of visible moisture training from the middle of an airliners wing. I assume this is induced drag created by wingtip vortices, when the aircraft is heavy, clean, and slow. However, I figured this would only happen at the “wingtips” and not from the middle section of a wing. I have seen them at the wingtips but a lot of the time it’s coming from the middle. If this is from the wingtip vortices how come they would come from the middle?

Any day when my #1 favorite gif in the whole world is actually relevant is to a question is a good day.

I disagree that it is a duplicate. The linked question does not really seem to address vortices from the flaps.

They are vortices coming from the flap panel, same as the vortices coming from the wing tip, but much more intense because the angle to the flow is so high.  Because of this, the pressure drop in the core of the flap vortice much more than pressure drop in the flow off the wing tip. This means the temperature drop is also much more, enough to condense the humidity in the air, like a horizontal tornado.

Very cool! I didn’t think about the flaps increasing angle of attack and creating more lift, thus intensifying the vortices. So would those technically be called “flap-tip vortices”??

The common term used for vortices at various places along the wing, but not the wing tips, is "trailing edge vortices".  In actuality, trailing vortices are being generated all along the wing, wherever the lift varies from neighboring wing sections. These vortices "roll outward" and combine with other trailing vortices until the combined voritces are "big enough" to roll off the wing. This can occur wherever there is a change in the wing's planform, but most often occurs at the edge of flap devices or the wingtip.

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text:
What does a helicopter "gas prod" gauge measure?
The beginning scenes of the movie "San Andreas" partly take place in a rescue helicopter. One of the panel gauges read "GAS PROD" above it. I googled it but didn't find much. Can someone explain what it does, and how it measures what's it measures? Thanks!

Related: Gas generator in a PT6 engine.

The instrument shows the gas generator rpm in the engine. It think you are referring to this scene (screenshot from youtube):

The Bell 412 in the movie uses a pair of Pratt & Whitney Canada PT6T-3BE Twin-Pac turboshafts, which are free turbine engines. The turboshafts used in helicopters consist of,

Compressor

Combustion chamber

turbine
and other components.

The gas producer (from which 'GAS PROD' came) forms part of the turbine. The gas generator forms the first stage that runs the compressor and makes the engine self sustaining. It also runs the oil and fuel pumps. As it is a free turbine, the gas generator stage is not mechanically connected to the next (power turbine) stage. From faasafety.gov:

The turbine section consists of a series of turbine wheels that are used to drive the compressor section and the rotor system. The first stage, which is usually referred to as the gas producer or N1 may consist of one or more turbine wheels. This stage drives the components necessary to complete the turbine cycle making the engine self-sustaining. Common components driven by the N1 stage are the compressor, oil pump, and fuel pump. The second stage, which may also consist of one or more wheels, is dedicated to driving the main rotor system and accessories from the engine gearbox. This is referred to as the power turbine (N2 or Nr).

In some cases, NG is used in place of N1. The gas generator speed is measured in the PT6 engines using a tachometer-generator mounted  on the engine.
From United turbine training Manual:

The tachometer-generator produces an electric current which is used in conjunction with a tachometer to indicate gas generator RPM. The tachometer-generator drive and mount pad are located at the 5 o’clock position on the accessory gearbox and is driven form the internal scavenge pump.

Except in this case, the gauge measures the intermediate turbine temperature.

@aeroalias Look at the left-most gauge, it says FUEL QTY on the panel and Fuel Quantity on the gauge.  The center and right-most gauge in the picture are labeled ITT on the panel and ITT in the gauge.  The label GAS PROD goes with the gauges not shown above the top of the picture.  This answer seems to correctly answer the question "what does a gas prod gauge measure", but the image really adds a lot of confusion; partly because the OP's question asks "what does gauge with GAS PROD above it measure", which in this case is ITT.

You have captured the wrong part of the instrument panel.  The gage you are showing is the ITT gage, while the Gas Prod is just above it, but you cropped it in your picture.  Go back to the picture, and crop it so that "Gas prod" is under the gage.  that will show the gas prod gage.  (As you can see, "ITT" is under the ITT gage that you are showing in the picture.)

That's an Inter Turbine Temperature gauge - measures the temperature of the gas exiting the high pressure gas core turbine and entering the low pressure power turbine.

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text:
I would like to find details of N41JA, an aircraft that flew in the 1970s
I acquired a large group of photo negatives this week mainly of aerial photos from the 1970s in the northern California and San Francisco area. One of the photos has a plane with number N41JA. I traced this to a company in Santa Rosa. My ultimate goal is to try and find the photographer.  I have dates that the photos were supposedly taken. Is it possible to match the plane to the dates and to a person? I am looking for any information that might help me or suggestions on how I might proceed? Thank you.

Also known as C-GTPB

that plane was operated by STOL Air Commuter, a small airline serving northern california from SFO International Airport in the early 1970's, now defunct.


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Where can I find (or how can I calculate) the glide ratio for a PA-28-181?
I'm filling out ForeFlight's new glide slope feature, and I'm trying to find the glide ratio for a Piper Archer II (PA-28-181). I know the best glide speed is 76, but can't find the glide ratio. Any help on where to find this?
Edit:
Below is the glide range graph from my PoH, and below that is the information ForeFlight is asking for. I'm not really sure how to read that graph to get a glide slope number.

This should be in the poh.

Thanks @acpilot just updated my question with what I think is the graph I need from the PoH, but not sure how to get the glide slop number off it.

About 9.5:1 on a standard day according to the graph (~11,000 gets you ~20sm). My rule of thumb for most GA planes is 8:1. I plan 7:1 to account for slop and maneuvering for landing.

Awesome! Thanks @acpilot

Answered here: https://aviation.stackexchange.com/questions/57262/how-to-calculate-the-best-glide-speed-if-there-is-none-on-the-poh/57263#57263

If you were to take off from an airport at 2,000' ASL on a standard day, and climb to 7,280' ASL you would be exactly 5,280' above the ground which means exactly 1 statute mile above the ground.
If you were to cut the engine, and then use the information available in the chart, you should be able to glide about 10 statute miles which yields about a 10 to 1 glide ratio.

Fantastic answer. Thanks.

You will have to obtain this from the Pilot's Operating Handbook for the particular aircraft you are flying.  Piper usually has a glide performance figure in the Perfeomance section of the POH.  Trying to calculate your glide distance or glide ration by other means and you are probably entering dangerous waters.

Thanks, I updated my question with the graph I think you're mentioning, and the ForeFlight box to give some context of why I'm trying to find the glide slope.

If I'm reading the chart correctly, the glide ratio varies with the ambient air temperature.  Therefore a standard glide ratio is not going to apply here.  I would be hesitant to trust your life to this ForeFlight feature and instead rely on a thorough examination and learn the the numbers from this chart instead of trying to create a uniform glide ratio for the airplane.

Totally agree. I just put in a 7:1 glide ratio, and will use the feature as one more tool in the event of an emergency.

To calculate your glide ratio, work the graph to obtain the gliding range and convert the NM to Feet. Then see how many feet you travel per 1000 feet drop. Whatever number you obtain divide by 1000.


text:
Has there ever been a report of a helicopter flying into a downburst?
I was recently flying my quadcopter and it started to go out of control. It was because I was flying it below a ceiling fan which acted as a mini downburst shoving the little quad to the ground.
So have there ever been reports of a helicopter accidently flying into a downburst?

Helicopters in general trade-off performance vs cost vs efficiency etc and do not have much "spare" power. A downdraft is going to result in a loss of contol in that you will not be able to maintain altitude or other axis. Helicopter pilots (and I suspect most GA pilots in general) avoid anything that might produce a downdraft. Mountain flying needs a particular set of skills and knowledge to conduct safely and knowing where downdrafts are likely to be encountered is a key part of that. Attempting to pull collective to maintain height is going to result in a loss of RRPM.

Yes, it would be really amazing if it had never happened. Since "reports" are only required in the case of accidents, here are extracts from three NTSB summaries:
WPR13CA155

During descent for an off-airport pinnacle landing, the helicopter
  encountered a downdraft about 75 to 100 feet above ground level (agl),
  and the pilot receiving instruction increased collective input. The
  flight instructor advised the pilot receiving instruction to be less
  aggressive using the collective as the flight continued to the landing
  area. As the helicopter descended through about 10 to 25 feet agl, it
  encountered a second downdraft, and the pilot receiving instruction
  increased collective again, which was followed by a decrease in rotor
  rpm.

ANC09LA098

During the approach to the 5,657 foot level site, the pilot said he
  encountered a downdraft as the helicopter approached the site, and the
  helicopter descended below his anticipated approach path. He initiated
  a go-around, but the helicopter continued to descend, and landed hard,
  about 150 feet short and down slope of his intended touchdown point.

WPR09CA470

As he flew the helicopter out of the leeward side of the peak, he
  encountered a downdraft. He maneuvered the helicopter toward a wide
  open valley that descended about 5,000 feet below. The downdraft
  pushed the helicopter into the face of the mountain, despite the
  pilot's application of full collective and descending flight into the
  valley.

beware flying on the leeward side of a ridge

@rbp Yea, that isn't a downburst, its just flow over a mountain.

I was addressing the third example


text:
Why is everything in aviation written in abbreviations?
please tell me if there is already a duplicate, I could't find one.
Why is like everything in aviation written in abbreviations?
ACARS Message:

/WND 275057/MCH 81/TRB LT CHOP /SKY UNDERCAST/ICE NONE

Why don't they just write:

Wind: 275 at 57 Knots. Light Turbulences. Not cloudy, No ice.

And also in the cockpit
HDG, SPD, ALT, LDG GEAR.
Of course, I know, its shorter and faster to read, but wouldn't it make such a bug difference if you write "Heading" instead of HDG?
Thanks, Noah

"its shorter and faster to read" you answered your own question. This information is aimed at people who understand it and it is unambiguous.  There is no need for it to be easier for people who do not understand it to read.

Actually the question is good. At first sight, there is no need to change, hence it will continue in the future. But there are so many abbreviations that were used  when Morse and  telex were the communication standards that have been discontinued, like the Q code in military and aeronautical activities... who still use QBH or QRX?

It might be possible to answer this, but only for very specific sets of abbreviations. The METAR topic has already been answered, but your question about abbreviations in cockpit displays (at least, I think that's what you mean) might belong in ux.SE rather than here. And of course, you could ask the general question "why so many abbreviations?" about almost any industry or technical activity. As Simon said in his comment, professionals in any area value concision and precision, both for efficiency and to avoid misunderstandings.

For the weather, those come from ye olde days of teletypes when it took a significant amount time to transmit characters. Yes, they should go away.


text:
How to balance the cargo on a plane with the wings further aft?
For example on an MD-88, is the center of gravity on the back of the plane because the empennage, wings and engines are located there? So they would have to put most of the cargo on the back of the plane?

Yes, the wing is positioned so that the center of lift is near the center of gravity. The MD-80 is very tail heavy due to the aft mounting of the engines. I have actually personally seen the nose of an MD-80 lifted off the ground by a jet bridge, and it didn't even hurt the door that was supporting the weight.
This chart is from the MD-80 weight and balance manual, which can be found on google. You can see that the center of gravity (CG) must be within -2.8% to 33.4% of the Mean Aerodynamic Chord (MAC) which is an approximation of average wing chord. So basically the CG must be in the forward 1/3 of the average wing chord, typically the center of lift is around 25% of chord. On the MD-80 the leading edge of the MAC is at body station 885.547, which is behind the actual LE of the wing at the fuselage.

The reason you want to place the CG near the center of lift is to create the smallest pitch moment possible between the CG and CL. The pitching moment created by the difference in the CG and CL location must be reacted out by the horizontal stabilizer. The more moment, the larger the stabilizer must be and the more inefficient the aircraft. Here is an illustration (stolen from this question How does a commercial airliner measure its weight/mass?):

Here is the picture of the MD-80 doing the wheelie:

Thanks for noting that your charts and drawings were "stolen from Google". However, siting the exact location they were "stolen" from is expected (it's nice to know whether they were actually stolen, or just borrowed). Otherwise, nice answer!

The chart is from the MD-80 weight and balance manual, as stated, technically the weight and balance manual is proprietary but can be easily from multiple legit sources on google. The drawing is from here: http://aviation.stackexchange.com/questions/16307/how-does-a-commercial-airliner-measure-its-weight-mass, I'll update the answer. The picture was taken by myself.

@OSUZorba What I don't understand is that if the heaviest part of the plane is on the back, where does the personnel have to put the baggage? On the nose to make a counterweight?

The plane was manufactured to be balanced around the desired center of gravity. It is the pilot (and ground crew's) responsibility to ensure cargo (including the self-loading kind) is distributed appropriately to maintain said CoG.

@kepler22b basically what FreeMan said. There are a lot of variables. For example on a short flight without much fuel they may have to load it more tail heavy. On a long flight with a lot of fuel, they may have to load nose heavy.


text:
Why are the cockpit windshields on the A350 black?
The newest planes like the 787 or A350 have a different kind of cockpit windshields:

Picture source
The A350 has "black" windshields:

Source
Does anybody know why are the windshields different?

Because they are coated to reflect nothing but infrared? From the inside they are transparent.

The pilots union has been demanding an "equipment allowance" for its members to pay for "personal equipment necessary to the profession", which turns out to be rather expensive but really cool looking sunglasses. This was cheaper.

On that 787 in the photo they actually look gold. Which makes me think of the gold windows on stealth aircraft as described in this answer but those are for radar reflection.

Pretty much all glass can look black, if it's brighter outside than in, and the angle's right.

The gold tint on the 787 window is a conductive coating for de-icing.

Dreamliner jet flight-deck crews will view the world through commercial aviation's largest windshields by PPG, kept clear of fog and ice with gold and indium-tin oxide heating systems. source

The A350 also has a windshield anti-ice system. It is referred to in this answer. One thing both aircraft have in common is that they use curved windshields. I'm not sure if that adds to the black look. But what does add to the black sunglasses look is that the window frames are painted black.

Source

Btw: There's a thread on Airliners.net where most of them seem to despise the black window frames.

When did Zorro become an A350?

The only reference regarding A350 I could find is:

The A350 XWB is the first aircraft to "wear sunglasses," referring to
  this jetliner’s distinctive cockpit windows.

Although from the inside, the view appears to be normal. It could probably be adjustable because on this article, you can see normal transparent windows from outside.


text:
Why haven't helicopter CAT III procedures ever been developed?
Why is there no helicopter equivalent to air transport CAT III ILS?  This PPrUNe thread discusses that some helicopter manufacturers have tested coupled approaches down to very low visibility minima (perhaps even zero-zero), but it seems that even with the current capability levels of autopilot technology and ILS ground station sophistication, there's no way for a helicopter to land in minima below RVR 1200'/DA 100' (i.e. the "half minima" rule applied to a standard ILS, or a COPTER ILS procedure).

Because many copter autopilots are capable of flying a Cat I ILS to 200AGL, and then descending on autopilot into a hover at a pre-determined altitude above the runway. The pilot can then descend down to the runway surface without any forward visibility. The radar altimeter is used to judge distance to the ground. Because of the unique capabilities of helicopters and their autopilots, Cat II and Cat III are superfluous.

There certainly are few operators who fly to the CAT II ILS minima, one of which is the Cougar Helicopters of Newfoundland, Canada. I know, since I was one of their pilots.
Forward visibility for the CAT II is 600 RVR.
The CAT III is not used yet due to the certification issues and few other problems, but I assure you that technology used in the Sikorsky S-92 A is quite capable of this level of service.
We most certainly can land on a long runway with worse conditions using the technique described by the RBP, not legally, but in an emergency - when no alternative is left - it could be utilized.
The S-92-B is in the plans now. Its Flight Director will have something called a Rig Approach as a standard feature.
It promises to bring the big Helibus to the near 0-0 conditions to any helideck in the middle of an ocean with no runway needed.

Good info - welcome to Av.SE!

In an emergency, anything you need to do is legal.


text:
What is this racetrack-shaped Special Use Airspace, and why isn’t it on the VFR sectional?
What type of SUA is AR633A, the cyan racetrack-shaped SUA north of Knoxville, Tenneessee (KTYS) depicted below on sua.faa.gov?
Why doesn’t it correspond to anything on the VFR sectional?

Re. your last point, the FAA page shows that the airspace is entirely in class A, therefore it's irrelevant to VFR flights. In fact, it isn't on any chart (at least on skyvector.com) including the IFR ones, but ATC will provide separation under IFR anyway.

According to this report on air crashes AR-633 (I assume the same as AR-633A now)

The cities of Oak Ridge, Knoxville, and Rockwood lie beneath AR-633, a
volume of airspace used by the 134th Tennessee Air National Guard Air
Refueling Group for practicing air refueling (Sect. 2.2). Although
under military jurisdiction, this designated airspace is equivalent to
an FAA holding pattern. AR-633 has an airspace volume of approximately
97 statute miles x 41 statute miles x I statute mile in depth.
Refueling operations take place within this box of airspace. Because
the military has jurisdiction over this volume of airspace and
operations may be considered sensitive, it is impossible to determine
whether refueling operations by the 134th Air Refueling Group occur
directly over the Oak Ridge reservation. The Oak Ridge reservation
encompasses an area of approximately 58 sq mi; the refueling area used
by the military (AR-633) encompasses 4,000 total sq mi.

The Text List Help for sua.faa.gov defines the AR Special Use Airspace type as

TYPE: AR - Aerial Refueling Route
DEFINITION: An aerial refueling route is airspace used by military tankers that routinely refuel other military aircraft along published altitudes (in most cases above 10,000 feet AGL).
PURPOSE: Aerial Refueling Routes are identified to inform non-participating pilots of the potential danger from activities being conducted. This airspace is not prohibited as long as other aircraft provide vertical or lateral separation from the refueling aircraft. Contact the assigned FSS for AR details.

The area highlighted in cyan in the question doesn't seem to correspond to the 97x41-mile area mentioned in this report, since 97x41 is an aspect ratio of about 2.5:1, whereas the cyan area is about 4:1. Or is it the grey area within the cyan area that we should be looking at?

The current area may have changed since that report was written. In the report is AR-633 and the question references AR-633A which may be the current amended version with new dimensions. However the location description puts it where the user is asking about.

This is indeed a designated air refueling track used by military tanker aircraft (all AR-nnn SUA areas are, and they all share that same general racetrack shape).
The reason why it isn't on a sectional is because it's simply not a concern to anyone who isn't in a high-performance, high-altitude airplane -- air refueling (of fixed-wing birds at least) typically takes place well into the FLs (FL280-FL330 is typical, although it may be lower or higher depending on what the tanker is gassing up), and doesn't bother anybody below.


text:
When should I slow to approach speed?
When do I have to slow to approach speed in order to qualify for a particular category? Specifically, if I want/need cat A minima, what is the exact point at which I need to be at 90 kt (or less)?
I’d assumed it was the FAF, because I can’t see how anything before that should affect your minima. My usual CFII says it’s the IAF, and another CFII says 3 miles before the FAF, but neither could cite a rule to support their position; it was just what their CFII had taught them.
(For the sake of argument, assume no legs are marked with explicit category restrictions, as I’ve seen on some teardrop procedures.)

I don't think there is a reg for that, it partly depends on the airplane I suppose. Dirtier (i.e. draggier)  airplanes slow down faster so you don't have to slow down as soon.

@GdD I’ve had ATC ask me to maintain max speed (~140) to the FAF. That’s fine with me since I can dump the gear/flaps and slow to 90 within a few seconds, but according to two CFIIs, it’s still not legal to call myself Cat A.

Specifically, I would say you have to be at category A approach speed before you descend below category B minimums.

A look through the U.S. Terps document (N8260.3E) states this:

The minimum PT distance is 10 NM when CAT B, C, or D minimums are authorized. Decrease this distance to 5 NM where only CAT A aircraft or helicopters are to be operating, and increase to 15 NM to accommodate operational requirements, or as specified in paragraph 2-4-5.d. No extension of the PT is permitted without a PFAF. When a PT is authorized for use by approach CAT E aircraft, use a 15-NM PT distance.
(page 2-23) (section 2-4-5)

2-1-7. Approach Categories. Aircraft performance differences have an effect on the airspace and visibility needed to perform certain maneuvers. Because of these differences, aircraft manufacturer/operational directives assign an alphabetical category to each aircraft (see 14 CFR Part 97). The categories used and referenced throughout this order are CAT A, B, C, D, and E. The authorized CAT must be used to determine OEAs [obstacle evaluation area] for circling and missed approaches and used to establish landing minimums. (page 2-5) (section 2-1-7)

My opinion is simply this:  If there is a required procedure turn, hold-in-lieu-procedure-turn (HILPT) or DME arc, these are all based on the category aircraft approved for the approach.  I would fly these segments at a speed lower than the maximum authorized category on the approach.
Once I cross the PFAF or FAF, I will fly a speed that does not exceed the category I am using for that approach.  For a stabilized approach, I will be at my VREF speed by 1000' AGL in IMC or 500' AGL in VMC and that will ensure I am in the category I need for the landing mins, circle and missed approach.
I found nothing in the TERPS that requires you to fly at VREF at the PFAF or FAF. You could cross at 200 KIAS if you wanted to or told to by ATC. You could slow down to VREF by minimums and be in the correct category... I suppose. I mentioned a stabilized approach for a reason, a great landing is preceded by a great stabilized approach. Am I willing to risk becoming unstabilized to fly faster and slow down by the (M)DA? I am not personally willing to do that... so I go with my previous statement. 1000' AGL in IMC or 500' AGL in VMC.

@StephenS I’d say, “Yes” because if you are able to slow to 90kts then you are flying a Cat A aircraft.  If you were in a Cat C aircraft you would be unable to slow to 90kts.

I found nothing in the TERPS that requires you to fly at VREF at the PFAF or FAF.  You could cross at 200 KIAS if you wanted to or told to by ATC.  You could slow down to VREF by minimums and be in the correct category... I suppose.  I mentioned a stabilized approach for a reason, a great landing is preceded by a great stabilized approach.  Am I willing to risk becoming unstabilized to fly faster and slow down by the (M)DA?  I am not personally willing to do that... so I go with my previous statement.  1000' AGL in IMC or 500' AGL in VMC.

I don't have an FAR reference to support this, but logically, you should be at category A approach speed before you descend below category B minimums.
But something else occurs to me. The concept of having lower minimums when approaching at lower speeds is flawed in this respect. It is based on the need to maneuver to avoid obstacles, perform circling approaches, procedures turns, etc. and assumes that maneuverability (primarily tun radius), is better the slower you fly. But, for any given aircraft in a given configuration, this is actually backwards. In actuality, The closer you get to stall speed, the less maneuverable you are - (See this question).
So, unless you artificially limit yourself to 10 or 15 degrees of bank, your actual maneuverability, and the category you should use should probably be determined more by your aircraft`s stall speed (or 1.3 x stall, to be fair), than by the actual speed you are flying.

@757toga, presumably then the distinction wouldn't matter, unless you are circling.

@757toga If the minima are the same, the question is moot, isn’t it?

Another comment that belies the entire concept here is this. The concept of having lower minimums when approaching at lower speeds is flawed in this respect. It assumes that maneuverability (primarily tun radius), is better the slower you fly. But, for any given aircraft in any given configuration, this is actually backwards. The closer you get to stall speed, the less maneuverable you are. The category you should use should be determined more by your aircraft`s stall speed (or 1.3 x stall,  to be fair), than by the actual speed you are flying.

It’s not maneuverability per se but standard rate turn radius, which does indeed vary with speed.

@StephenS,  Yes the key phrase there is standard rate. Can you perform a standard rate turn (that's 3 deg/sec) at approach speed? Not without stalling I would bet.

@CharlesBretana At 1.3*Vso (50-60kt), it’s not fun, but any PPL should be able to do it without stalling. At the speed I actually fly approaches (90kt+), no problem at all.

You might make a little tighter curve by using steep bank while flying faster, but that is only an emergency escape maneuver—the risk of losing spatial orientation or altitude control is too high. For normal approach it is recommended not to exceed 30° bank and maintain minimum maneuvering speed 1.4×Vs while maneuvering may be required (you can do 30° bank at 1.3×Vs without stalling, but the margin is getting a bit tight then). Under those constraints the assumption turn radius is larger when flying faster is warranted.

@Jan, Agree with your numbers. My only complaint, (if you could call it a complaint), is that the way the topic is treated and discussed often leaves GA pilots with the incorrect assumption that slowing down in critical situations will improve your turning performance.

In the airline world, even with the weather at mins, it's common to be assigned "170 to the marker".  That would make us all Cat E, and plenty of approaches don't have Cat E mins published. A few only have Cat C and not Cat D. So unless there is some waiver, your speed at the marker is NOT what matters.
A good CFI should know better than quoting "what I was told" as if it had regulatory weight per se!
Your AFM or OpSpecs or POH should tell you when you have to be at V-Target; the approach categories deal with what that speed is, not when it happens, AFAIK.

There are two reasons to slow to the approach speed for the category of aircraft you are flying. Visibility on straight-in approaches and the protected area on a circling approach. The AIM 5-4-7 Instrument Approach Procedures directly addresses when you should be at the approach speed for your category of aircraft for a circling approach. Basically, you want to be sure that you don’t fly outside of the protected area when maneuvering for a circling approach.

In addition to pilot techniques for maneuvering, one acceptable method
to reduce the risk of flying out of the circling approach protected
area is to use either the minima corresponding to the category
determined during certification or minima associated with a higher
category. Helicopters may use Category A minima. If it is necessary to
operate at a speed in excess of the upper limit of the speed range for
an aircraft's category, the minimums for the higher category should be
used. This may occur with certain aircraft types operating in
heavy/gusty wind, icing, or non-normal conditions. For example, an
airplane which fits into Category B, but is circling to land at a
speed of 145 knots, should use the approach Category D minimums. As an
additional example, a Category A airplane (or helicopter) which is
operating at 130 knots on a straight-in approach should use the
approach Category C minimums.

For straight-in approaches the logic is the same, but it is not spelled out in the AIM. The faster the airplane is flying the less time the pilot has to avoid obstacles and see the runway. If there is a difference in visibility by category for descent below the altitude of the FAF it means that the aircraft will not be able to see the runway at the MAP and make a normal approach to landing. I would say that neither CFII is right and the speed has to be maintained at and after the FAF.

This assumes a fixed speed. But what if I slow down during the approach?  For instance, say I pass the FAF at 140 but slow to 90 before reaching the Cat C DA. Can I then continue down to the Cat A DA?

@StephenS, ask yourself this: what would the rationale be for going missed approach at the Cat C DA if you were then flying at a Cat A approach speed?

@MichaelHall A good question, and I have none. That’s why we’re here. But I don’t like citing common sense alone when i have multiple CFIIs telling me I’m wrong.

How does the quote support your conclusion? It doesn't say anything about FAF, only about the actual circling (which happens below DA/after MAP).

@StephenS, but you aren’t “wrong” unless proven so by your CFIs, who don’t even agree!  I understand why you are asking, and it is a good question, but those two have an obligation to know when they are teaching a technique vs something covered by regulations.


text:
What is the difference between SBAS and SBAS PA mode on my FMS?
We have a Collins FMS, and in the GNSS control page it tells you what mode it is operating in.
In the instance that I checked it, it said "SBAS PA". The flight manual said that it can operate in "SBAS" as well, leading me to believe that there is a difference between the two. The flight manual said nothing else on the subject of the different modes, and a Google search didn't turn up anything. Is there any documentation on GNSS receivers having these two different SBAS modes?

SBAS PA = Precision approach. Navigation integrity is assured by a satellite-based monitoring system like the WAAS system, and the monitoring meets requirements for SBAS approaches (LPV) as described by RTCA/DO-229.
SBAS = Integrity is assured by a satellite-based monitoring system, but doesn't meet RTCA/DO-229 requirements for precision approaches. You'll have to stick to more traditional approach types.
I'm honestly not sure when plain "SBAS" mode applies, and my GPS manual doesn't provide much clarification. It could be your procedure isn't loaded or hasn't gotten all the information it needs like the FAS block.  It could be when you're outside the precision approach region, or outside the service area for the satellites even though you can see the satellite, which is pretty common but I think you shouldn't even be in SBAS in that case. It could even be the case that there are SBAS satellites that support position corrections but not approaches - I don't think as of this writing that Japan's MSAS supports LPV.


text:
Why is this plane struggling to gain altitude?
Here in this video, you can see an airplane trying hard to gain altitude (happens at 1 min 17 secs, original video):
Plane Gets Struck By Lightning
I am skeptical. Does it actually happen, or is the pilot or autopilot doing it on purpose? In my opinion, these are the potential causes:

In this scenario, we may conclude that the lift is lower than it would be if the plane were flying normally.
The weight can also be greater than the maximum takeoff weight  (MTOW).
The pilot may not have activated the flaps.
This can also happen during an icing condition on wings.

Am I correct?

Significant icing only occurs in visible moisture (fog, cloud, drizzle or rain), but here it's sunny with no clouds in sight, so icing can be ruled out.

A bigger question stems from the second video linked... for the jet that is hit by lightning... is that the pilot's real nose?  Looks like he borrowed it from the Concorde.

According to the video's information:
EMB-721 Sertanejo heavy and insane takeoff in Carlos Prates
This is

"EMB-721 Sertanejo heavy and insane takeoff in Carlos Prates.
Full fuel, 6 on board plus luggage
Copilot was 0 hours, crystallized and kept pulling the youke [sic].  Cpt took over, lowered his nose and managed to fly."

Basically, the inexperienced pilot miscalculated or misread the takeoff speed, and lifted too early, too hard.
Then when the plane just wallowed, he kept pulling back thinking that the laws of physics would make an exception for him if he kept on insisting hard enough. The captain was yelling: “Leave it to me. Stop pulling the yoke!”. The captain took over control, lowered the nose just a bit to allow airspeed to build up, and then gained altitude.
P.S.: One does wonder about the wisdom of giving a pilot with zero hours on the plane, the role as takeoff pilot from that airport in those conditions.
Heavy plane, crosswind takeoff, utterly unforgiving runway runoff (the runway runoff is a cliff leading to densely populated urban area, including condos!), and multiple passengers, including screaming kids.

The EMB-721 Sertanejo is a Piper PA-32R built under licence in Brazil.  https://commons.wikimedia.org/wiki/Category:Embraer_EMB-721_Sertanejo

The Carlos Prates airport elevation is 3,044’ and the runway is only 2,848’ long. That is pretty marginal for a heavy PA-32 on a hot day.

"crystallized " = "froze"?

Copilot: "I can't hear myself think, we must be at vR." - Captain: "Someday they won't scream and we're gonna roll right over the edge."

@PcMan Weird. You were able to edit your own question before but not any longer? Also: The quote doesn't appear to have been substantially altered, Peter Mortensen just made one quote of the two (unless you meant that the first sentence "Leave it to me" was from the co-pilot, holding on to the stick, but you said "captain").

Unbelievable. How close are they to the roofs in 0:20-0:25? And at 0:49 they are flying between high-rises. Absolute madness. You can't get closer to a crash and not crash.

@Peter-ReinstateMonica well, the airport itself is a bit scary. Having a short runway, zero runoff area, and the non-runoff-area being mixed commercial and residential zoning, just down a cliff from the runway end? I wonder if those are part of the reason that airport is being closed in may this year.

Looks overloaded for the temperature/altitude conditions. With all the yapping and chattering, it sounds like the cabin was full.  Once out ground effect, its rate of climb appears to have been around 50 FPM.
The shadow of the tail looks to be a Piper Cherokee, and the engine sounds like a 6 cylinder engine, so I'm guessing it's a Cherokee 6, way overloaded for that particular departure. The engine sounds fine.
Some decent flying skills were applied there, balanced on a knife edge of performance or lack thereof, to make up for some horrible judgement.  He was a couple of knots away from descending instead of (barely) climbing.

Agree with John K. This is a profoundly scary video to watch.

Per the other answer, you guessed the plane correctly. Amazing!

In this scenario, we may conclude that the Lift is lower than it would be if the plane were flying normally.

A low climb rate is not caused by lack of lift.  A lack of lift would cause the plane to accelerate downward.  Lift is actually slightly less than weight in a steady climb.
A low climb rate is caused by excess drag, i.e. by a lack of excess thrust compared to the drag vector.
For more, see this related ASE answer: Does lift equal weight in a climb?
One source of excess drag is that the wing is being operated at an excessive angle of attack (AOA).  Taking off overloaded from a short runway, failing to apply takeoff flaps, and ice on the wing which decreases the lift coefficient at any given angle of attack, would all be possible reasons why a pilot might find it difficult to keep the plane in the air at a more normal angle of attack, as suggested in the question.
And as suggested in several answers, the only way out of such a situation is to avoid the temptation to raise the nose too high, and allow the plane to accelerate to a higher airspeed.
Pilots often use "lift" in a way that really means something more like "climbing capability".  If we really want to analyze what is going on in terms of the underlying physical forces, we have to remember that "lift" is not the same as "climbing capability".

the only way out of such a situation - Of course avoiding the possibility for the situation in the first place is the only safe way to fly.  Better training.  Less load.  Fly in appropriate weather conditions.  They nearly killed themselves and the people living in those homes.  Hopefully a license or two will get pulled...

Wow, that's a scary story.  I once had an experience in which the pilot instructed us to all urinate/defecate (outside of the little aircraft) before trying to take off.  We immediately decided to hike ourselves out instead of going up in the air with that pilot.  Unrelated, I had an experience where I felt like an idiot for not taking the keys away from a friend who was driving once I realized he was drinking.  I was sleeping in the back seat and woke up to see him drinking... it was many, many years ago, but I still feel like an idiot for not insisting he immediately pull over.

@quietflyer The real cause of this incident is low take-off speed. So we can say Lift is less due to less take-off speed. How drag is greater due to take-off speed? Lift is upward force. So high lift means high force in an upward direction and high climb rate. Correct me if I am wrong.


text:
Do pilots need a different license for each type of aircraft?
I have heard before that even an experienced Boeing 747 pilot can't operate a Boing 787 Dreamliner without attaining the specific license first.

Related: Why do some aircraft require type ratings to fly them?

FWIW: The controversies surrounding the rollout of the 737 Max had a lot to do with pilot training.  Boeing really wanted pilots with a 737 type rating to be able to fly a 737 Max without retraining.  That would give them a big leg up on the competition (aka AirBus).  But, they did make changes, to things that pilots didn't expect and then things went very wrong.

This is why when one pilot is incapacitated and someone from the cabin volunteers to help out in the cockpit, the helper is usually operating the radio rather than flying the aircraft. Radio skills are largely the same across different aircraft.

@757toga I am curious, even when the 757 and 767 share a type rating, is this ever done in practice?  Meaning, while you meet the technical requirement of 61.31 from the FAA perspective, would an airline still require a distinct training curriculum for each aircraft?

Not a different "license" but a different "type rating" - a subtle, but important, distinction.
Although a 747 and a 787 have the same basic controls, controlling them through all phases of flight, with full understanding of the limitations, procedures, and emergency actions differ enough that specific training is required for each
When an aircraft becomes "suitably complex" (decided by the licensing authority) then a separate "type rating" is required

Further to Jamiec's answer, a type rating can be quite a significant endeavor.  For instance, moving from a being a 737 captain to a A321 will take about 3 months, almost all of which is systems training.  Because of the workload and focus required to complete the transition in 3 months, an airline will normally pull the pilot from flying status in their old aircraft while they undergo training in the new aircraft.

In many countries, there is a Class Rating that covers many different Types. In my (Australian) experience, newly licensed pilots are officially allowed to fly any aircraft having a single piston engine and maximum take-off weight less than 5700kg (12,500lb), with fixed pitch propeller, and fixed undercarriage with nose-wheel steering.
With further experience and testing, a pilot may have the fixed-pitch or fixed-undercarriage restrictions removed.
Once you want to fly a multi-engine aircraft, a turbojet, or a bigger plane, you'll typically need a specific rating for that exact aircraft.
There can be exceptions. For example, there was an aircraft with twin centre-line thrust piston engines that I was allowed to fly without a specific type rating. The most challenging part of flying a twin-engined aircraft is dealing with the off-centre thrust if one engine fails. If both engines are centreline-thrust (one at the front, and a "pusher" at the rear), then there is not such a challenging asymmetric situation when one fails.
The specific regulations (e.g. Australian tend to be quite wordy.

You will need a different rating, if the aircraft in question or different categories in classes. A person who holds a pilot certificate with a airplane single engine land rating, for instance, may not serve as PIC in a rotorcraft helicopter without a rotorcraft helicopter rating added to their pilot certificate, or received additional type specific training and signoffs per §61.31(h).  These are US regulations but ICAO has similar ones as well.  In addition for large aircraft, you will need to be type rated on the individual aircraft in question in order to operate them as PIC or serve as a required pilot flight crewmember.  You are also required to requalify every 12 months on type ratings in order to operate said aircraft.
So to your original question, a person who has a current type rated for required pilot flight crewmember duties on a Boeing 747 cannot perform the same duties on a Boeing 787, 737, etc. without being type rated on those aircraft as well.


text:
Is there an aerodynamic reason for airship fins to be at the tail?
I've read this interesting Stack Exchange question about why airships have fins:
Why do blimps have fins?
Which has me wondering why the fins are almost always located in the tail section.
After some digging, I can see practical benefits, compared to putting the fins in the middle: ground clearance and avoiding the gondola.
But is there an aerodynamic reason too? After all, planes, helicopters, arrows all seem to similarly have stabilisers at the tail.
Would the airship be less stable or harder to control if the fins and control surfaces were in the middle? Or even at the front? If so, why would that be?

Because if they were sat in a shed elsewhere, they wouldn't work at all.

@Richard I wish someone had told me that before takeoff

Many is the time I've looked at a question on this site and thought to myself "I hope they're not typing this as they come in to land"

Yes.
With fins in the middle the airship would be impossible to control. In order to work, fins need a lever arm with respect to the center of gravity. The longer, the better.
Almost all air vehicles are controlled by creating forces at a distance to the center of gravity, which in turn result in moments which allow to control attitude and direction. Airships are no exception.
While fins at the front would also create moments, they would increase the instability of the hull. Placing them at the rearmost position reduces this instability, which makes control easier. Still, airships are unstable and need constant attention by the crew. Making the fins large enough to give the airship natural stability would need much larger and heavier fins. The size of airships makes their eigenmodes slow enough so that manual control is possible.

Ok, that makes so much sense now you explained it to me, thanks!

Simply put: airships have fins mounted on the tail, the same reason  arrows have fletching on the tail and the same reason pub darts have fins on the tail.  For static and dynamic stability, the center of pressure from control fins must be aft of the center of mass.

@drrob - lots of things would start to make sense if you played KSP.

Note that "active" fins are perfectly fine at the front, though a little rarer - known as a "canard layout".

@MikeB ... only when computer controlled, with sufficient redundancy. This requires more weight and energy than a manual control. BTW; a canard also has natural stability due to the large wing in the back. Fins at the front do not yet make a canard.

@CarloFelicione Note that airships are not stable, despite the fins. They would need to be much larger to make the ship stable. All they do is to reduce instability and allow to control the ship.

@PeterKämpf  Wow - I did not know that the Wright brothers had computer control!

@MikeB Come on, Mike, do you really have to sink that low? Or did you not read until "a canard also has natural stability due to the large wing in the back"?

@Mazura playing KSP is an excellent idea. Didn't expect a genuinely good excuse to play games, so thanks :)

@MikeB, they didn't have a stable aircraft, either.  Keeping a Wright Flyer in the air was a constant battle against the aircraft's natural tendency to flip tail-first.


text:
Can anyone find Putins Il-96-300PU july 17 flight map?
Can anyone find Putin's Il-96-300PU July 17 flight track?
Putin's flight path has not been publicized on the internet. The Russian media is claiming that his aircraft would be in danger of being shot down, but has not shown that he would be even over Ukraine.  Initial information indicated that he was flying through Poland.
Is there a flight track for Vladimir Putin's aircraft on July 17?

It's an interesting question, but I'm not sure if it belongs here.

it doesn't. Maybe on politics.se or conspiracytheories.se (if that existed, it would make a great place to move about half the topics of several other se sites).

Its what Russian media is telling since July 17. So its their official Politics. But never showing flight path on RossijaTV or RT or any media news.


text:
Is there an aircrew bunk in the 747 cockpit?
Reading this article, I came across the quote :

Pilots also enjoy its creature comforts: at BA the 747s are known as
  the ensuite fleet. “Our little bedroom is within the cockpit: you can
  stick your pyjamas on and clean your teeth without anyone seeing you.
  And coming out the bunk when you wake up, it’s a different light and
  you’re in a plane cockpit in the sky,” he says.

I know there are crew sleep areas on large aircraft but I've never heard of there being a bunk.
Does anyone have a floor plan for the cockpit which would illustrate how do they fit those cabins there?

Related: How do pilots rest on long-haul flights?, though that's about sleeping quarters that are not in the cockpit.

The crew rest area is often bunks. Bunks = beds stacked above each other, which is the most space-efficient way to squeeze several beds in small area when it has normal walking height (on 747 it does).

Yes, there is a crew rest with two beds (bunk) connected to the cockpit on the 747. As MainMa notes, this can be found on 747-400 or 747-8 models, but not the older models. It can be seen on the seating charts here:

The crew rest is directly across from the two lavatories. While the lavatories open into the aisle of the cabin (grey area), the crew rest opens into the cockpit. There is a layout here that shows a how the upper deck is arranged. It's a freighter, but is was converted from a passenger plane, so it has the same crew rest location.
With the introduction of the 747-400, the position for the flight engineer was removed (seen below), with those functions being replaced by computers. This opened up a bit of room behind the pilot seats.

Source

The answer depends on the precise model of Boeing 747.
For instance, the Boeing 747-8 (third generation of 747) features two beds which are clearly visible here, in blue:

The original image of the complete aircraft is available here.
The setup is very close to the one shown in fooot's answer. In the same way, Boeing 747-400 has two bed as well, as can be seen on this schema.
On the other hand, the much older Boeing 747-300 doesn't seem to have any beds:

See the original image here
Other sources (including the detailed 8300x3800 cutout of Boeing 747-100) confirm that there are apparently no beds on older Boeing 747-100, 747-200 or 747-300 models.

Really nice picture of 747-8. Is there one with higher resolution available where one can read the text?

@Farhan: unfortunately, I couldn't find a higher resolution of the cutout, and given the numerous logotypes (FlightGlobal where the image is hosted, Spirit Aerosystems, Flight International, Boeing and General Electric), it is not even clear what is the original source of the cutout. Note that the red and orange colors of the model correspond to the the ones Boeing used for demo models in 2011 (see here), and not to a specific company.

Isn't fifth generation correct for 747-8?

@Peter: -100, -200, and SP were first-generation, -300 was "1 1/2 generation", -400 was second-generation, -8 is third-generation.

I found it difficult to find a specific floor plan.  I've seen references that the 747 had a lot of different plans, with many airlines having a crew rest area in the rear of the upper deck rather than off the cockpit.
No floor plan, but there are several location with photos available of the  rest area on the -8.  CNET has one.
No longer on the Boeing web site, there is an archived copy of the crew rest area for a -400 freighter that has a floorplan for the area.
This page isn't as detailed, but shows the crew rest area on a 747 to scale with more of the upper deck.  Unfortunately it lacks detail with how it connects to the cockpit.
And not a 747, but here is a page with a graphic of the 787 crew rest area.


text:
Should "mayday" be preferred over "SOS" in an emergency?
I was asked about the difference today. The only difference I know is that mayday doesn't appear in the exams ( like the SOS parts of the book, you get the joke? :) ). I also found the difference in the origin, but:

What is used in aviation? Both are equivalent or there is actually a difference and the one should be preferred over the other?

SOS is a distress signal. In the context of aviation emergency calls it would be equivalent to a Mayday call, which is the standard voice signal for distress.
There is, as far as I'm aware, no standard equivalent for an "urgency" (pan-pan) situation in morse code.

As far as its use in aviation, most aviation communication today is by voice (radiotelephone), and "SOS" is not generally used in voice communication.
Its used by morse code stations is because it is a short and easily recognized pattern:
. . . - - - . . .
Its recognizability is part of the reason it replaced the old Marconi CQD general distress call code
- . - . - - . - . - . .
which was literally a general call to all stations (CQ) signaling "distress" (D).
I can't find a reference, but I would assume there's at least one case in history where the SOS code was used by an aircraft (back when morse stations were common on aircraft).
An SOS signal could of course be transmitted today using the unmodulated carrier from your radio by simply keying the microphone, but that would only be useful if the voice circuit of your radio has failed and you had no other means to communicate. Otherwise voice contact or setting your transponder to an appropriate code would generally be the preferred way to signal distress.

CQD is -.-. --.- -.. in modern (ITU) Morse code. -.-. --.-. -.. might be CĜD if https://en.wikipedia.org/wiki/Morse_code#Letters,_numbers,_punctuation,_prosigns_for_Morse_code_and_non-English_variants is to be believed. It's probably close enough to be recognizable, but it's not correct.

The "SOS" prosign is for use with telegraph (typically Morse code) transmissions.
"Mayday" is for voice (radiotelephony) transmissions.
Therefore, as long as your radio(telephony transmitter) is working, you should use "mayday" if in your judgement doing so is required. "SOS" should not be used on radiotelephony. Saying "ess ooh ess" or, Heavens forbid, Sierra Oscar Sierra, might get you some attention in spite of that, but I can see no reason whatsoever to go out of your way to use nonstandard phraseology when a perfectly good (and internationally recognized, and drilled into one's head from early training) standard alternative already exists.
If for some reason your radio isn't working, then squawking 7600 or possibly 7700 and simply executing the proper loss-of-communications procedures for the airspace you're in is likely to be better (and will certainly be more readily recognizable) than trying to signal SOS via an intermittent, unmodulated AM carrier, which will come across as little more than clicking to anyone listening.
Your radiotelephony training and examination should have covered emergency communications, including the use of mayday. Mine certainly did, both on the theoretical as well as the practical examination. Thankfully thus far I haven't had to use that in real life.
Compare the extensive discussion in Why do airplanes use MAYDAY when in danger but ships send SOS?


text:
How do you cope with an asymmetric flap extension?
How do pilots cope with an asymmetric flap extension? What are the procedures for this type of occurrence which I suppose are similar on all aircraft?

On the jets I fly, it is either extremely unlikely or the manufacturer has made it so the flaps can only be split up to 7° before the flap computer stops flap rotation.  I was once told, that if you make some change to the airplane and  you don't like what just happened, then undo that change.  Seems like good advice to me.

@wbeard52: What is the aviation equivalent of git revert? I'm really hoping that it's not git rebase, especially if there are other people on that branch (passengers)!

@dotancohen rebase is not quite as severe in an airplane. It just means it's now based at a different field. :)

While not an asymmetric extension, I did fly a 172 once that the flaps wouldn't fully retract, they were a couple degrees out. Most noticeable during flying was a reduction in speed. Most airplanes you can also slip to try to reduce the air going over that flap since the flaps are located near the wing root.

I'd guess the procedures probably vary considerably by class and type. If the flaps on one side broke or got stuck on the light GA plane I mostly fly, the procedure would be to just set the side you can control to the same as the side you can't control and land with that amount of flaps. You can land it with no flaps; you'll just have to land a little faster than normal and with sub-optimal visibility of the runway (but still plenty to get the plane onto it safely.)
At least in the planes I've flown, it would be nearly impossible for the flaps on both sides to get stuck in different positions (because both sides are mechanically connected to the flap lever,) but even that could be dealt with by using the ailerons to counter the asymmetry of lift.
The other procedure involved is to do a proper pre-flight and make sure your flaps aren't broken, loose, or damaged before you leave the ground. :)

This will vary between small planes and large planes as a result of the flap extension mechanisms and how they can possibly break. This recently happened to my instructor and we had a long discussion about it so...
Before we dive in, it should be noted that the FAA recommends that while in the traffic pattern you do not extend the flaps while banking, in the event of an asymmetrical extension it may push you further into the turn.
In smaller planes (GA sized stuff) there are 2 basic flap mechanisms, electric and mechanical. The common Piper Cherokee line (all the way up through the early saratogas) employed a Johnson bar and all mechanical flaps. On the contrary Cessna moved the 172 to electrically driven flaps early on in its production.
As for what to do this will depend on how it fails. In the Piper there are retract springs in the flaps so if the extension mechanism fails the flap will remain in the retracted position. Generally what fails on the pipers is the bolt that holds the push rod onto the flap or the nut comes off due to a faulty pin although the cables can fail as well. The rod looks something like this

(Source)
Edit: I went flying this morning and got a picture of the flap pushrod joint on the Piper Warrior I was flying to show it in action. Here the flaps are fully deployed (3 notches) during my preflight check. As you can see checking that joint is critical, and you should always inspect to make sure the pin is properly in place through the nut. In this case you are looking at the head of the pin so its a bit hard to see but its there.

In any case generally speaking releasing the Johnson bar will retract the other flap and you will make a no flap landing (runway provided). In this instance if you have the fuel it may be advised to divert to an airport with a longer runway. You should also practice some no flap landings during you training for this very reason.
In the electric planes if any of the extension mechanisms break and you can still retract the flaps adhere to the procedure above. However in this case you could also have a drive motor failure or other electrical issues. For this you may be stuck with your flaps in a partially extended state. Some amount of aileron deflection will be required and you should expect higher landing speeds. Again diverting to a longer/wider runway may help. Care should be taken in the pattern turns in this case as well.
Considering the redundancy in commercial airliner systems this is less of an issue for larger planes. On top of that since large planes generally have multiple engines you can take advantage of differential power settings as well as cross control. Large planes also generally have more than one set of flaps that are often powered by multiple sets of hydraulic pistons which are unlikely to all fail in tandem. While you can have an asymmetrical extension on a commercial airliner chances are it would not be like that of a GA plane where you run the risk of a full extension on one side and no extension on the other.

(source)

On the Boeing aircraft I fly the flaps and slats are both fitted with an asymmetry protection system. When an asymmetry is detected the flap motors are stopped and you are stuck with the flap/slat where it is. If its the slats that are stuck you can still move the flaps with the alternate system and vice versa.
The (Quick Reference Handbook) QRH advises the actions necessary in using the alternate system and the reference landing speeds required, depending on at what stage of extension or retraction the asymmetry occurred.


text:
Do commercial lavatory suction systems create pressure mechanically or naturally?
Modern Boeing and Airbus aircraft employ a suction system for the lavatory on board. How is this suction system powered? By utilizing an on board suction pump or natural pressure and velocity difference from outside the aircraft during flight?
One way to find out would be to try a flush while plane is on a taxiway, but access to the lavatory during that period is not allowed.

Maybe that's why it's not allowed? :)

I'll add that I often see people using the lavatory while the plane is still at the gate -- flight attendants could prevent it if they wanted to by locking the lavatory doors, but in my experience, it's allowed (though they do get cranky if passengers don't finish up by the time they are ready to push off from the gate since all passengers have to be seated). If the toilets were inoperable on the ground, the lavatories would quickly become a health hazard when passengers are stuck in the plane during multi-hour ground delays.


text:
Could improper deplaning of a flight with full fuel tanks cause the plane to tip?
Reading this article regarding an Alaska Airlines 737 Flight that had to turn around back to the gate. There was a following statement:

At the gate, passengers were unloaded five rows at a time, to minimize the risk that the plane would tip under extra weight of fuel.

My general understanding is that the fuel tanks are usually placed near the COG (wings, cargo tanks). Assuming the tanks are still full, why would unloading of passengers all at one time possibly cause the plane to tip? Or is this bad reporting?

I dont know about fuel or this aircraft type in particular. But i have seen occasions where smaller aircraft (most recently a metroliner) tip backwards onto its tail because the baggage was loaded before the passengers boarded so i wouldnt be suprised if this was theoretically possible.

Totally off topic, but that article speaks volumes for Alaska Air! My son will be stationed in Fairbanks, AK in about a year, and they just moved to the top of the list of choices!

@FreeMan I've always heard great about Alaska Air, wish I could take them more but unfortunately SFO is a United / VA hub

As an aside, I've seen a non-flying 727 at a museum with its rear fuselage tipped to the ground due to ice accumulation.

The 737-900ER has (two) auxiliary fuel tanks in the aft cargo compartment, behind the wing (and center of gravity) with ~3400l capacity for increasing range (from 2800nm to 3,200nm).
In usual conditions, unloading of passengers wouldn't be a problem as the fuel would've been used up; However, as this was an overweight landing with full fuel tanks (the auxiliary fuel tanks weigh ~ 3t), the crew are just being cautious to prevent any incidents.

I see. Just as a followup, at what point do they fill the fuel tanks? I was always assuming the pumping started prior to passenger boarding, which would lead to a similar risk

I don't know what the procedures are on a 737 but some aircraft have their front gear tethered to the ground so it can withstand a certain amount of cog shift without tipping. That was done when loading cargo containers into a FedEx DC-10 since it would be tall heavy while the first several cans are loaded.

Many transport aircraft (including 737 derivatives) are designed with hard points in the tail structure. These hard points support a "tail stand", which is little more than a post to prevent tipback during loading/unloading. See this photo for an example. link

The 737 had a tendency to tail tip as can be seen here and here. They were just being diligent and of loading people in a timely and organized manner to avoid that. You can read up on it here as well.

Sounds like the second link you provided of the Magala incident wasn't due weight distribution, but actually due to the airbridge moving up while the L1 door was open! http://www.pprune.org/rumours-news/335905-sterling-b737-incident-malaga.html


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Why are the 737 trim wheels located so close to the seats?
I recently had the opportunity to try a 737 simulator and one thing that struck me was the placement of the trim wheels. They are located dangerously close to the seats and, man, do they spin fast. I can only imagine the pain if you accidentally leave the manual trimming handle retracted or if you get some hair stuck in there.
Why are they placed this way? I would assume that a less prominent placement would still allow easy access for manual trimming.

Here is a video I found.

To remind pilots to follow their checklists and stow the trim handle when not using it?

Here's another view of the trim wheels in action so you can see where the pilot's leg is in relation to the wheel. (Hair shouldn't be an issue, and it's safe with the handle stowed, but it can catch you in the knee if someone uses the electric trim with the handle extended.)

Instructional video, but not for a NG, showing the full chain from the trim wheel to the horizontal plan.

My guess is that the manual trim wheel handle (when not motor driven) to adjust it manually needs to be:

easily accessible from the seat.
generate a sufficient amount of torque by moment arm.

Which leaves this as one of the few spots where it could be conveniently placed. You can find the same thing in older aircraft cockpits including the L1011, B727 and B747-100/200. The 737 design remains very unchanged from when it first flew.

It is a good position in terms of motion efficiency: On the pedestal next to throttle/slats/flaps (all things which would require you to re-trim, and if the electric trim fails you're doing it with the wheel, so your hand is right there). The location (and noise the trim wheel makes) also provide audio and visual cues to the crew that the trim is running.

The noise is also perfect for waking up sleeping jumpseaters to let them know you are starting descent :)


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What is the measurement system used in the aviation industry?
I saw this question from History Stack Exchange and noted that the US is still using the imperial measurement system such as feet, miles and pounds.
Given that a plane may need to fly from one country to another, is there any standardisation across the globe? Does planes manufactured by Boeing use one system and planes made by the Airbus another system? If not, wouldn't it be very easy for pilots to make calculation error?

What about the literal nuts and bolts? I assume they are all metric? Is there anything in aeronautics engineering that is still imperial?

Actually, the US uses American customary units. The American fluid ounce is slightly different from the imperial one but the more significant differences are that an American pint is 16oz (imperial is 20) and, correspondingly, an American gallon is ~20% smaller than imperial; an American hundredweight is 100lb (imperial is 112, despite the name) so an American ton is 2000lb (imperial is 2240)

Outside US, SI is generally used for everything except altitude, distance and speed.

Altitude: 1000 ft happens to be reasonable vertical separation, which is somewhat easier to calculate with than the corresponding metric figure 300 m.
Distance: There are two quantities that were never converted to decimal. Time and angle. Since we didn't switch to gradians, it makes sense to keep nautical mile, which corresponds to 1 minute along meridian or equator, as it makes calculating distances from navigational maps somewhat easier. If the maps were marked in gradian coordinates, 1 gradian would be 100 km and kilometres would be used.
Speed: Obviously based on the unit of distance in use.

In Russia, Commonwealth of Independent States (most former Soviet countries) and China (and I am not sure whether some other Asian countries), metric system is used for everything. I believe in Russia they recently switched to flight levels based on feet, but they do use metres below transition altitude.
Before second world war, aircraft built in continental Europe usually had instruments in metric units as well. However before the war aviation was more advanced in the USA, instrument procedures were developed in USA and after the war there was surplus of US-built planes, so most of the world just adopted the US procedures including the units they used as everybody using the same units was more important than any personal preferences. Without these reasons we'd be probably using metric in Europe for everything too.

SI actually specifies the radian, not the gradian, as the unit of angle.

@DavidRicherby: Yes, but I said angles were not converted to decimal, not to SI. Radian would be impractical for latitudes, longitudes and bearings.

For altitude, I once saw a argument telling there is no advantage of meters over foot, and no advantage of foot over meters: if we use meters, the reasonable vertical separation easy to calculate would be 250m, and the only reason we choose one over the other was the prevalence of US-built aircraft. I don't know what to think of this argumentation.

@ManuH: Sure it is. That's what I said in the last paragraph too. I also added to the last paragraph mention of the US procedures, since instrument rules were developed in US.

I can tell you that all of the airplanes that I have flown (which are US registered, but some are French built) use the following:

Feet for height
Knots for airspeed (Nautical Miles/Hour)

Some old airplanes still use Miles/Hour (MPH)

Nautical Miles or feet for distance
Statue Miles or feet for weather (visibility and RVR)
Mach for high speed flight
Inches of Mercury for altimeter settings

Most of the airplanes that I have flown can actually switch between "hg and hPa (mb).

pounds/square inch for pressure
Pounds for the fuel quantity on the aircraft (read by the fuel gauges)
Pounds/hour for fuel flow
Gallons to order/purchase fuel

These are pretty standard in most of the Americas (North/Central/South), but in certain parts of the world some of the units are different:

Meters for height
Kilometers or meters for distance and weather
HectoPascals (hPa/Millibars) for altimeter settings
Kilograms for fuel quantity on the aircraft
Kilograms/hour for fuel flow
Liters to order/purchase fuel

Russia, CIS countries and China are the main notable exceptions that use the metric system I believe.

@Manfred For altitude, yes.  For altimeter settings, and runway distance, visibility, etc metric is far more common.

All METARs I've seen anywhere outside America had metres for visibility and hectopascals (=millibars, but hPa is more common name) for altimeter settings.

@JanHudec Canada and Mexico both use SM for visibility, and both of those plus South America use "hg for the altimeter.  The Bahamas and most of the Caribbean are the same.

@Lnafziger: That's why I said America and not USA.

@JanHudec Oh, well that's what I said in my answer do I thought that you were pointing out something that you didn't agree with.

@Lnafziger: I was pointing out that the "some parts" is really all except Americas.

@JanHudec Perhaps, but as soon as we say all someone will point out a place that doesn't comply....  I rarely use always or all when talking about aviation. :)

American vehicles have had their speedometers graduated both in miles and kilometers for just about forever. Also, over the past few decades, more and more American cars are using metric sized fasteners.

Mainland China is the only country that uses meters for altitude. Russia switched to feet almost 20 years ago. Feet are just a better unit for the task due to vertical separation needs and such. All that really matters is keeping things consistent and with easy to remember round numbers (ie. Even thousands westbound, odd thousands eastbound. And 1000 meters would be excessive.)

Unless Boeing has recently changed to the metric system in their design work, the short answer to the question as to whether Boeing and Airbus use different systems insofar as aircraft manufacture is yes. I'm only familiar with Boeing up through the 747-400. Perhaps others can provide an answer for later models.
The Boeing Weight and Balance Control and Loading manuals I have do provide kilogram pages following the pound pages, but that the pound is the controlling unit is also stated.
Interestingly, for moment limitations, the manuals follow the inch-pound pages with inch-kilogram pages. In other words, they're mixing systems, which I believe to be unwise as the net effect is to introduce a third, hybridized system.
In the past, many 747 freighter flights that I flew were slightly over gross at takeoff due to the fact that the common conversion used for kilograms to pounds was 2.2 when the actual value is 2.20462262.
As I remember, only the U.S. and Liberia are still non-metric officially. There is a political dimension to this which you can explore at http://en.wikipedia.org/wiki/Metrication_in_the_United_States.

2.20462262, says Google.

Burma is also non-metric, though they're making moves towards metrication.

inch-kilogram is not just mixing measurement systems, it's actually the wrong unit for a moment. Kilograms measure mass; a moment is a force at a distance, not a mass at a distance. The correct (but still weirdly mixed) unit would be the inch-Newton.

A common misconception is that pounds and kilograms, or nautical miles and kilometers are similar units. They are not actually measuring the same thing. The pound is a unit of force not mass, kilogram is a unit of mass not force.(newtons are the SI unit of force, and slugs are the "imperial" unit of mass) kilometers and statute miles are units of fixed distance and do not cleanly divide into the Earth-geoid's circumference, nautical miles are a fixed integer fraction of the circumference. What matters most to an aircraft(which tend to have minimal acceleration once air born) is not the mass but the lifting force, drag force, and motive force(thrust).
As for nuts and bolts etc, all that matters is that an industry standard, "size B" just needs to be consistent between makers and batches, the units used to measure the tolerances of a size B make no difference. The set of standards to be used is purely one of economics, this is why all plumbing in buildings around the world is based on inches, it is a standard so all spare parts fit and mass production makes it low cost. That is what counts, that you call a pipe one inch, 26mm, or size 37G doesn't change the fact that it has a known diameter tolerance thread pitch, thread form, and is compatible between manufacturers.
When it comes to machining many machines have, for example, set gear ratios for either metric or SAE forms (maybe carriage movement per rotation of a lathe) and these are very costly machines that last for many decades so just switching may not be cost effective, especially if all the machines need to switch at the same time. American auto makers attempted to mix metric and inch withing single vehicles during the '70s and '80s to ease the transition costs and it was a nightmare for maintenance mechanics.(really one of the several reasons for the downfall of Detroit)
The issue is eg a 12mm screw is very close to a 1/2" screw, close enough for general strength but not close enough in thread shape to interchange but too close in size to notice by eye. Also you need two full sets of tools to cover the same size/strength range.

Hmm... Wikipedia (and general usage) disagrees about pound: mass is lb, force is, strictly speaking, lbf. (Similarly kg and kgf). Of course, the standard unit is N, but more often than not kg (implicitly kgf) is preferred. As for nautical mile, it had been originally defined as a fraction of Earth circumference (likewise the metre!), but the current official definition is 1852 m exactly.

Wikipedia is not a solid authority. The label lbf is used for clarity.
Kgf is a crude approximation it is not a defined base unit, the newton has a proper definition: the force needed to accelerate one Kg by one meter per second per second. A pound-force is the amount of force required to accelerate a slug at a rate of 1 ft/s^2

"  No name has yet been given to the unit of mass and, in fact, as we have developed the theory of dynamics no name is necessary. Whenever the mass, m, appears in our formulae, we substitute the ratio of the convenient force-acceleration pair (w/g), and measure the mass in lbs. per ft./sec.2 or in grams per cm./sec.2. "
— Noel Charlton Little, College Physics, Charles Scribner's Sons, 1928, p. 165.


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On a 777 what would happen if the aft pressurization switch was accidentally left closed?
The Boeing 777 has fore and aft pressurisation switches (see example here). If the aft switch was forgotten on takeoff, could this cause a loss of cabin pressurisation when the aircraft reaches altitude?

My question was edited and the point of it is now lost. My basic idea is: Is there any MISTAKE the pilots could have made that would have done in all the rest of the pasengers without the pilots noticing it until it was too late? The rest of the flight characteristics would then make sense....

There would most certainly be a visible alert on the screen that it had been left in the close position, since this is not the normal configuration, and the pilots would have seen that. Otherwise, they would also have gotten plenty of warnings about cabin pressure had it been too low.

So it can't be pressure. What about the air conditioning? Somewhere in the "Source" document, I read that passengers are airconditioned from both sides but the flight deck just from one (I think that it was the left).

if it was unintentional, any deviation from the normal operation of the pressurization the pilots would have been alerted about problems on multiple levels. This was most probably a deliberate act by the pilots, where they might or might not have switched off the pressurization entirely.

From my previous source in that incapacitation question:

Two outflow valves are installed: one forward and one aft. Normally,
  most of the outflow is through the aft outflow valve. This improves
  ventilation and smoke removal. Cabin altitude and full ventilation
  rates can be maintained by either valve. Source

There is only one pressurization system for the whole aircraft. The two outflow valves regulate the airflow moving through the cockpit and cabin respectively, the intake air comes from engine bleed air, which is quite hot, and is mixed with outside ambient air to regulate the temperature through two or more heat exchangers, depending on the make and size of the aircraft. If there were two pressurization systems, one for the cockpit and one for the cabin, there would have to be a pressure bulkhead between the cockpit and the cabin, and there isn't.


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Why are row numbers 10 and 11 skipped on Frontier's A-319?
I'm sitting behind an exit row (the exit row is row 12), but am still not sure why rows 10-11 are missing from this plane. Note the number goes from 9 to 12.

Why are the rows numbered this way? It's the same on both sides.

Also notice how you're in row 14, right behind 12?

No, I'm in row 13. All the other rows are sequential.

Interesting. I've never seen a row 13 on an airliner (I suppose many buildings have no 13th floor for the same reason)

A random check of seat plans reveals row 13 appears often enough, right there between 12 and 14.

Airline row numbering has more to do with fleet consistency than sequential numbering in one airplane type.
Head over to SeatGuru and look up Frontier. They fly 3 types of mid-size narrowbody - A319, A320, Embraer E190 - and not surprisingly row 12 is an exit row in each one. The E190 and A319 don't have row 11, only the A319 is missing row 10.
It's the same reason 2+2 seating skips seats B and E ( AC DF ), where 3+3 seating goes all the way across ( ABC DEF ). Widebody aircraft have a different sequence because it doesn't need to match - the same cabin crew will rarely work both major classes and they don't tend to run regional airlines on widebody (long-haul) routes.
Look at Air Canada's fleet - row 18 is the beginning of economy and an exit row in almost the entire widebody fleet (the exception is probably historical).

Just to add some context, this is often done for the benefit of staff and frequent flyers, both of whom know without checking that row 12 is the exit row with the nice extra leg room - and can deliberately choose that row or avoid placing children etc in that row (as the passenger needs to be able to operate the exit)

@JonStory Additionally, if there is an equipment change, this scheme means you'll usually end up with the same type of seat.


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How many alternates should I prepare PPL checkride cross country?
I have a PPL checkride and the first portion of the exam is a long cross-country journey of about 300 miles. I know I'm expecting a diversion in there somewhere. But in general and for checkride purposes, how many alternates should I prepare?
In my opinion, I'd think one alternate for every 30 minutes of flight. Because, if there was some issue such as losing my alternator, then I have about 30 minutes left on the battery.
Is this the right way to think about it?

in the united states

Please keep in mind that what your examiner wants to see is how safe a pilot you’ll be after you pass your checkride.  The planning you do should therefore be a realistic representation of what that will look like.
I don’t research every airport along my route for every flight, nor do I evaluate alternates at all for VFR flights. I do try to keep my route near airports when possible in case a diversion is necessary, and they make great VFR checkpoints too (a habit I picked up before GPS), but I don’t look any deeper than that, nor did my instructors or examiner expect me to.
If something does go wrong, then you quickly decide the best place to divert based on how urgent it is to get on the ground; a fire may have a different answer than a passenger needing a restroom or unforecasted weather ahead, for instance.  The examiner will want to see you use all resources available (sectional, EFB, glass panel, ATC, etc.) to make that decision live, like you would on a real flight, not checking an unrealistic canned list of diversion points.
Note that if you planned your route to fly over/near airports (see above), the answer is usually going to be pretty obvious, which is another reason to do that.  Worst case, crashing at an airport (which should have fire/rescue services readily available) is probably more survivable than crashing somewhere else.

Maybe a little bit better way to approach this problem is not so much preselect in a series of alternates, but as part of flight planning and periodically assess during the flight where, if something happens are you going to go and what contingency plans are available to you.
Keep in mind that an alternate course of action is going to be your best course of action available to you given the circumstances. That may or may not be an airport. For instance, and examiner may opt to put you in a situation where no airport is available to you and see how you react, either in a simulated situation with the aircraft boxed in by storms or have an in-flight emergency were a power off glide to the nearest airport is simply not possible. These are some contingencies that you need to think about for alternate courses of action. Now an examiner might give you a scenario where an alternate airport is available to you, for instance a fuel urgency situation, and see if you select another airport nearby and evaluate your decision making process for selecting this, the criteria you used to evaluate this and make your decision, etc.

("and examiner" → "an examiner")


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Is there a tailwind limit while in cruise?
The storm Ciarán is, as of posting, making its way through the Atlantic Ocean with winds easily passing 300 km/h (161 kts).
While this is going on, a BA flight took only 8 h 45 mins to do LAS-LHR with a tracked speed peaking at 1200 km/h (~mach 0.98).
I know that, for landing, tailwind, must not exceed a certain value...
Is there such a limit to how much tailwind a cruising plane can experience?

How would they know?

@DJohnM, GS > TAS.

"Mach" values are really only appopriate for airspeeds, not groundspeeds.  (Unless you are trying to imply that the groundspeed of the aircraft was .98 the groundspeed that a sound wave would have, moving in the same direction as the plane, at the same altitude, under the same conditions....  but that's just a complicated way of saying that the airspeed was .98 Mach.)

Related: Can a jet stream make a subsonic plane fly at a supersonic speed relative to the ground?

300 km/h looks like a typo. Isn't it 200 km/h?

@PeterMortensen It's not, look at mins answer

I'm adding another answer to the good one already posted, only to mention some aspects relative to winds in altitude.

Groundspeed vs airspeed
You're talking about groundspeed, speed relative to the ground. But when an aircraft is not taking off or landing, this reference is meaningless.
Air rotates with Earth, meaning when there is no wind air already moves at Mach 1 at 45° of latitude, and is still at the poles, at sea level, a bit more at 10 km height. Adding 300 km/h is adding only 30% only.
Aircraft always fly in this moving air and what counts is the difference between air and the aircraft, what is called airspeed.
For the aircraft this makes no difference air is moving or not, exactly like the fact Earth is moving in space is meaningless for us if we are seated in our kitchen.
So to answer your question: There is no limit at all because there is no impact on the aircraft.
There is an exception for the takeoff and landing phases, where the aircraft depends both on air for being aloft, an the ground to accelerate or brake. If air is moving relatively to the ground, this must be managed, and there are limits, in particular for crosswind, and tailwind. These limits, which are quite small numbers, are defined by the operator, based on the maximum value demonstrated by the manufacturer, e.g. on the A330, Airbus demonstrated a crosswind of 32 kt and a tailwind of 10 kt, but some operator will limit it further.
Wind in altitude
There is a second aspect to your question: Storm wind velocities are given for sea level, but winds at 10 km are very different.
It happens Ciaran strong winds are the left over at sea level of higher currents at the tropopause (10/12 km): Sea this view of the winds at sea level:

The storm is closing to the English channel, and now the rest of the Northern Atlantic is pretty calm at sea level. The location at the circle has now a wind of 38 km/h, but at an altitude of 10 km (250 hPa), winds are really different:

Now we have a wind of 325 km/h at the same place. These data and images are from earth.nullschool.net. So the question is what are winds in this area when there is no storm?
Jet stream
The answer is West-to-East winds are regularly at 200 km/h at cruise altitude, they form the jet stream around the North pole:

This pink/white oscillation denotes winds between 200 and 300 km/h at this time and this is pretty the same other days.

Is G force not applicable and relative to ground speed? This is probably irrelevant for straight-and-level flight, but would it make a difference if one needs to alter course? Is it to small (given standard turns for non-military or non-acrobatic flight) to be consequential?

"G-force" is a measure of acceleration. Acceleration is a change in velocity over time. It does not matter what reference that velocity uses - an acceleration of 1m/s/s is the same force whether my starting velocity is 0 or 9999km/h.

@StephanSamuel: James is right. Perhaps the only "force" which matters is Coriolis effect, a fictitious force. It makes depressions and anticyclones spiral in presence of acceleration (due to the air mass at different heights/latitudes, so at different tangential velocities), but has no measurable effect on an aircraft.

@StephanSamuel: A plane turns relative to the air.  If you had a 100 kt tailwind going east, and then turn 90 degrees left to a point the nose due north, your ground speed will have a 100 kt eastward component.  Since you aren't killing this part of your horizontal speed, it doesn't make the turn require any extra G forces.  Unless you turn more tightly to make your ground track more like it would have been without wind.  So if you fly the same, the G forces will be the same, but your ground track will have an extra component in the direction of the wind.  Effectively a wider turn.

@StephanSamuel: Perhaps relevant to look at coast guard search patterns (https://www.youtube.com/watch?v=aoXJfuPaFF8 - Smarter Every Day) - ocean current drift speeds are comparable to the water speed of the boat, so this can have a large effect.  Destin's video includes plots of a search pattern in absolute lat/lon coordinates vs. in coordinates relative to a drifting buoy (datum).  Exact same situation: you don't know anything's different due to surface current except by measuring your position relative to the ocean floor / shore / GPS coordinates, rather than the water.

Even if I have no pilot's license, I'd say no limit for Tail Wind in Cruise, for sure tail wind is absolutely undesirable in takeoff and landing.
During cruise, there is no 'tailwind', unless wind has a higher speed than aircraft top speed, a rare event, that may induce loss of lift. Did it ever happen?
The airplane floats on a wind that takes it forward at a higher speed respect to ground. That's all, folks!

"During cruise, there is no 'tailwind', unless wind has a higher speed than aircraft top speed, a rare event, that may induce loss of lift. "  -- incorrect, because the aircraft flies inside the wind and thus does not feel the wind.

This is what I said. Isn't it?

Only the pilot in an old open cockpit flying machine 'feels the wind'. Sorry, Airplanes have no senses, no 'feelings'. A semantic issue. Aufwiedersehen. Gesund +